Alzheimer's disease is characterized by the aggregation of beta-amyloid (Abeta) protein in the brain, widespread neurodegeneration, and cognitive decline. Our work focuses on amelioration of Alzheimer's pathology by reducing or eliminating GD3 synthase (GD3S), an enzyme responsible for synthesis of two of the four major brain gangliosides. Our preliminary data demonstrate that knocking out the gene that codes for GD3S (St8sia1) drastically reduces A2 aggregation and oxidative stress, and prevents memory deficits in mice carrying mutant human transgenes for amyloid precursor protein (App) and presenilin 1 (Psen1). However, GD3S is absent from birth in these mice, and they lack many of the gangliosides involved in normal development. Our goal is to understand the role of gangliosides in Alzheimer's disease and how they relate to memory impairment, the earliest cognitive symptom of the disease. The objective of this application is to determine whether knocking down GD3S using gene silencing (shRNA) is as effective as knocking out GD3S in alleviating features of Alzheimer's disease in the 5xFAD mouse model. The general hypothesis of the proposed research is that shRNA knock-down of GD3S will successfully reduce plaque formation and prevent neurodegeneration and memory impairments in adult mutant mice. We have already made three viral- vector-mediated GD3S-shRNA constructs that reduce GD3S expression ~80 percent and persist in the brain. In the proposed experiments, shRNA constructs will be administered to 5xFAD and control mice. Spatial memory will be assessed, as well as control tests for anxiety and sensorimotor function. Post-mortem analyses will assess Alzheimer- related neuropathology and cell death. Successfully reducing amyloid burden, cell death, and memory impairment in the transgenic mice may provide insight into new treatment strategies for Alzheimer's disease--treatments that could reduce or prevent dementia in Alzheimer patients.